1. Field of the Invention
Embodiments of the present invention generally relate to apparatus and methods for use in a hydrocarbon wellbore. More particularly, the invention provides apparatus and methods for completing hydrocarbon wells. Still more particularly, the invention provides apparatus and methods for forming a sidetrack wellbore from an existing wellbore that has a substantially uniform inner diameter with the existing wellbore.
2. Description of the Related Art
In the drilling of a hydrocarbon well, the borehole is physically lined with strings of tubulars (e.g., liner or casing) to prevent the walls of the borehole from collapsing and to provide a reliable path for well production fluid, drilling mud, and other fluids that are naturally present or that may be introduced into the well. In a typical liner operation, after the well is drilled to a new depth, the drill bit and drill string are removed and a string of tubulars is lowered into the well to a predetermined position whereby the top of the string is at about the same height as the bottom of the existing string of tubular. Thereafter, with the new string of tubular held in place either temporarily or with some mechanical hanger, a column of cement is pumped into the tubular and forced to the bottom of the borehole where it flows out of the tubular and flows upwards into an annulus defined by the borehole and the tubular. The two principal functions of the cement between the tubular and the borehole are to restrict fluid movement between formations and to support the tubular and borehole.
To save time and money, apparatus to facilitate cementing are often lowered into the borehole along with the tubular to be cemented. Cementing apparatus typically includes a number of different components made up at the surface prior to run-in. These include a tapered nose portion located at the downhole end of the tubular to facilitate insertion thereof into the borehole. A check valve at least partially seals the end of the tubular and prevents entry of well fluid during run-in while permitting cement to subsequently flow outwards. The same valve or another valve or plug typically located in a baffle collar above the cementing tool prevents the cement from back flowing into the tubular. Components of the cementing apparatus are made of fiberglass, plastic, or other drillable material, that, like cement remaining in the tubular, can be drilled when the cementing is complete and the borehole is drilled to a new depth.
Historically, each section of tubular inserted to line a borehole was necessarily smaller in diameter than the section of tubular previously inserted. In this manner, a wellbore was formed of sequential strings of tubular of an ever-decreasing inner and outer diameter. Recently, methods and apparatus for expanding the diameter of tubular in a wellbore have advanced to the point where it has become commercially feasible to utilize the technology. This has led to the idea of monobore wells wherein through the expansion of tubulars in the wellbore, the wellbore remains at about the same diameter throughout its length. The advantages of the monobore well are obvious. The tubulars lining the borehole, and therefore the possible path for fluid in and out of the well remains consistent regardless of well depth. Additionally, tools and other devices can more easily be run into the well without regard for the smaller diameters of tubulars encountered on the way to the bottom of the wellbore.
In a monobore well, a first string of tubulars is inserted into the wellbore and cemented therein in a conventional manner. Thereafter, a string of tubulars having a smaller diameter is inserted into the wellbore as in prior art methods. However, after insertion into the wellbore the second string of tubulars is expanded to approximately the same inner and outer diameter as the first string. The strings can be connected together by use of a conventional hanger or, more typically, the smaller tubular is simply expanded into the interior of the larger diameter tubular thereabove in an area where the tubulars overlap.
With the advent of monobore wells, certain problems have arisen. One problem relates to maintaining the monobore when a sidetrack is necessary. Current methods of expanding tubulars in a wellbore to create a connection between tubulars require the application of a radial force to the interior of the smaller tubular and expanding its diameter out until the larger tubular is itself pushed passed its elastic limits. The result is a connection having an outer diameter greater than the original outer diameter of the larger tubular. While the increase in the outer diameter is minimal in comparison to the overall diameter, there are instances where expanding the diameter of the larger tubular is difficult or impossible. For example, in the completion of a monobore well, the upper string of tubulars is preferably cemented into place before the next string of tubulars is lowered into the well and its diameter expanded. Because the annular area between the outside of the larger tubular and the borehole therearound is filled with cured cement, the diameter of the larger tubular cannot be easily expanded past its original shape. Further, damage to the cement may occurred when such expansion is performed.
Therefore, a need exists for a method of maintaining the monobore when a lateral wellbore is formed.